Some basic questions about PETSC

[Ben Tay]

Hi,

regarding qn 4 ie  the requirement of VecAssemblyBegin,VecAssemblyEnd, I
used VecPlaceArray, VecResetArray to change the values. I did not use
Assembly after the 1st time step and it works ok. So that is fine too,
right?

Thank you!

On 12/4/06, Satish Balay <balay at mcs.anl.gov> wrote:
>
> On Sun, 3 Dec 2006, Matthew Knepley wrote:
>
> > > 1. Are petscscaler the same as real nos.? I am writing in double
> precision
> > > or real(8). So are these 2 interchangeable? (same as petscint and
> integer).
> >
> > Yes.
>
> You can check these defines in include/finclude/petscdef.h
>
> PetscInt -> integer*4
> PetscScalar -> real*8
>
> >
> > > 2. while linking in compaq visual fortran, I get the warning message
> about
> > > conflict library with LIBCMT. Is it important or can I just ignore it?
> >
> > This is determined by your configure. Satish will know better how to
> control
> > it.
>
> There are some warnings because of the way compqaq f90 tries to
> workarround some bugs in Visual Studio 6 version of the libraries. It
> will be fine as long as all code [PETSc & application] is compiled
> with the same set of compiler options,
>
> >
> > > 3. I am writing in f90 free form format. When I modify from fixed f77
> format
> > > to f90, it gives me a lot of error, which seems to be the include file
> > > error. So, is it possible to write in f90 format?
> >
> > Depending on which compiler you use, you might have to give a flag. For
> g95
> > it is -ffree-form.
>
> We'll have to see the error messgaes to determine what the problem is
> - however - if you check the PETSc fortran examples - they comply with
> both fixed and free from syntax.
>
> > > 4. I am writing a Navier stokes solver and I'm using PETSC to solve
> the
> > > poisson eqn. If only the RHS changes with each time step, do I need to
> call
> > >
> > > VecCreateSeq
> > > <insert values in RHS b>
> > > VecAssemblyBegin
> > > VecAssemblyEnd
> > > VecDestroy
> > >
> > > at each time step? I don't think I can (or I should) change values of
> b
> > > after VecAssemblyBegin,VecAssemblyEnd, or can I?
> >
> > You can just change the values. Call AssemblyBegin/End() after each
> group
> > of changes.
>
> Another note: - If you change values with VecSetValues() - you'll need
> to call VecAssemblyBegin,VecAssemblyEnd. However if you do
> VecGetArray() [or VecGetArrayF0()] - and change values - then you
> don't need the calls to VecAssembly...
>
> Satish
>
>
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